The present invention relates to the planarization of semiconductor wafers using a chemical mechanical planarization technique. More particularly, the present invention relates to an improved system and method for cleaning and rinsing residual slurry from semiconductor wafers during the chemical mechanical planarization process.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. Wafers are commonly constructed in layers, where a portion of a circuit is created on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on the wafer, an oxide layer is put down allowing the vias to pass through but covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer that must be smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer carrier that brings the wafer into contact with a polishing pad rotating in the plane of the wafer surface to be planarized. A polishing fluid, such as a chemical polishing agent or slurry containing microabrasives is applied to the polishing pad to polish the wafer. The wafer carrier then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer.
Following the polishing and planarization operation, the wafer carrier is lifted off of the polishing pad and retained in a conveyor that is used to transport the wafer and wafer carrier. The external surfaces of the wafer carrier and the face of the wafer are typically coated with the residual polishing fluid and the material removed from the wafer surface during the operation. These materials are typically removed using deionized water (D.I. water). Presently known methods of material removal involve manual spraying or a head diametrical wash system. Manual spraying is accomplished with a spray hose that is manipulated by an operator of the CMP system.
The head diametrical wash system comprises fixed holes that are included on the conveyor. The holes surround the upper portion of the wafer carrier when it is retained in the conveyor. The holes are piped to a D.I. water supply that is pressurized to spray D.I. water out the holes and onto the outer surface of the wafer carrier. The D.I. water flows by gravity down the outer surfaces of the wafer carrier and across the horizontal face of the wafer that is mounted on the bottom of the wafer carrier. The D.I. water containing the materials rinsed from the wafer carrier and wafer then forms into droplets that drip from the wafer down onto the polishing pad and elsewhere in the CMP system.
Known problems exist with these rinsing and cleaning techniques. Specifically, the manual spraying is time consuming, manpower intensive, generates overspray on other parts of the CMP system and may provide non-uniform results. In the case of the diametrical face wash, the washing action lacks scrubbing effect. In addition, the flow of the D.I. water across the face of the semi-conductor wafer is non-uniform since it depends on the molecular attraction of the water to the surfaces of the wafer carrier and the wafer. The non-uniform flow of water may contribute to non-uniform washing of the wafer. This is especially true as the diameter of the face of the wafer is increased. Further, the D.I. water containing the residual polishing fluid and the material removed from the wafer surface is allowed to run into the CMP system thereby contributing additional foreign materials and particulate to the CMP process.
Accordingly, there is a need for systems and methods of rinsing and cleaning wafer carriers and semiconductor wafers that is automatic, efficient, thorough and capable of being contained.
To address the deficiencies of the prior art, methods and systems are described herein that are capable of automated operation in a CMP system to provide a uniform, thorough and efficient cleaning and rinsing of a wafer carrier and a semiconductor wafer mounted thereon. A presently preferred embodiment comprises a head spray assembly that is moveable between a parked position and a spray position. In the spray position, the head spray assembly is adjacent a wafer carrier that is detachably mounted in a conveyor.
The head spray assembly is capable of sealing to a portion of the conveyor surrounding the wafer carrier prior to activation of a plurality of spray nozzles disposed therein. Upon activation, the spray nozzles discharge pressurized liquid thereby causing the spray nozzles to rotate. The liquid discharged from the spray nozzles is discharged through an opening in the head spray assembly and is in liquid communication with the wafer carrier and the semiconductor wafer thereon. The rotating spray action of the discharged liquid cleans and rinses the wafer carrier and semiconductor wafer. The liquid that washes the wafer carrier and the semiconductor wafer is contained due to the seal with the conveyor and is channeled to a drain for transfer out of the CMP system.
Other features and advantages of the invention will be apparent from the drawings and the more detailed description of the invention that follows. The foregoing discussion of the preferred embodiments has been provided only by way of introduction. Nothing in this section should be taken as a limitation on the following claims, which define the scope of the invention.